TOKYO - Anti-whaling activists chased Japanese ships in Antarctic waters and the crew of one Japanese vessel held two protesters who jumped aboard.

There were reports Benjamin Pott of Australia and Giles Lane of Britain, who reportedly boarded the Yushin Maru No. 2 Tuesday, were tied to the mast, but Japanese authorities in Tokyo denied them.

Activists have vowed to disrupt the annual whaling expedition, the Voice of America reported.

The drama began after the activists from the anti-whaling group Sea Shepherd boarded the Japanese vessel from their own boat "The Steve Irwin." Their group said the two wanted to deliver a letter urging the whale hunt be stopped, and described their detention as kidnapping, the report said.

The Japanese said the pair attacked crewmen with bottles of acid.

A whaling fleet spokesman said the illegal boarding was an act of piracy.

The letter carried by the activists said the whaling in the Southern Whale Sanctuary violated laws of Australia, which opposes the whale hunt, the Independent said.

The newspaper said the incident came after an Australian judge enforced a ban against the Japanese company involved in the whale hunt in Australia's exclusive 200-mile economic zone, which Japan does not recognize.